The present invention is directed to suppression of fluid-borne noise in fluid handling systems, such as in automotive power steering, power brake, fuel and air conditioning systems.
There are many applications in commerce and industry in which it is desirable to suppress fluid-borne noise in fluid handling systems. For example, in automotive applications, it is desirable to suppress fluid-borne noise generated by the pump or load in power steering, fuel distribution, air conditioning and power brake fluid systems. It is also desirable to suppress compressor noise in domestic and commercial air conditioning systems. Fluid-borne noise can also be a problem in industrial hydraulic applications in terms of both generation of audible noise, and wear and fatigue of system components.
Kumar, xe2x80x9cSmart Materials For Acoustic or Vibration Control.xe2x80x9d Pennsylvania State University (1991) teaches that fluid-borne noise within a metal tube can be suppressed by positioning a piezoelectric actuator at one end of the fluid tube. The piezoelectric actuator is disposed between an aluminum block that is affixed to the tube and an aluminum block that is coupled to a rubber membrane in contact with the fluid. A sensor is disposed between the actuator and the membrane block, and is coupled through a frequency selective preamplifier, a phase shifter and an amplifier for energizing the piezoelectric actuator 180xc2x0 out of phase with the predominant frequency of vibration within the fluid.
Although the subject matter taught by the Kumar thesis addresses problems theretofore extant in the art, further improvements remain desirable. For example, an important consideration in high-volume applications, such as automotive applications, is that the unit be economical to manufacture and reliable over an extended operating lifetime. One object of the present invention is to provide a system and method that satisfy these objectives. Another object of the present invention is to provide a system and method of fluid-borne noise suppression in which a single unit configuration can be employed in a variety of applications. For example, in one implementation of the invention, it is an objective of the invention to provide a system and method for suppression of fluid-borne noise in automotive power steering systems in which a single unit design can be employed in conjunction with a wide variety of power steering systems. Another object of the present invention is to provide a system and method that are characterized by low power consumption.
Apparatus for suppressing fluid-borne noise in a fluid conduit in accordance with the various preferred embodiments of the invention includes a vibration sensor for operative coupling to the conduit for providing an electrical sensor signal as a function of fluid pressure fluctuations in the conduit. A piezoelectric actuator is adapted to be mounted on the conduit for imparting pressure fluctuations to fluid in the conduit. An electronic controller is responsive to the sensor signal for energizing the actuator 180xc2x0 out of phase with fluid pressure fluctuations sensed by the sensor. The sensor may be either closely coupled to the actuator, or separate from the actuator and disposed upstream of the actuator with respect to the direction of fluid flow through the conduit. The sensor in the preferred embodiments of the invention comprises a piezoelectric sensor, and the actuator comprises a stack of piezoelectric elements.
The electronic control unit is responsive to frequency components of pressure fluctuations of fluid in the conduit for energizing the actuator as a function of the amplitude of the frequency component of greatest amplitude. The sensor is responsive to fluid pressure fluctuations in the conduit over a broad frequency range, much lower than the resonant frequencies of the sensor and actuator. The frequency range in the preferred embodiments of the invention preferably is from zero to at least 1000 hertz.
A fluid handling system in accordance with another aspect of the present invention includes a conduit for conducting fluid under pressure and an apparatus of the character described above for suppressing fluid-borne noise caused by fluid pressure fluctuations in the conduit. In various embodiments of the invention, the conduit includes a volumetric enlargement to which the sensor and actuator are coupled, or a right-angled turn at which the sensor and actuator are disposed in opposition to fluid flowing through the conduit. In another embodiment of the invention, the actuator comprises a plurality of annular discs disposed within the conduit in such a way that fluid flows through the discs. The sensor is either closely coupled to the actuator, or is separate from the actuator and disposed upstream of the actuator with respect to the direction of fluid flow through the conduit. In one preferred embodiment of the invention, the conduit includes an opening, and the noise suppression apparatus of the invention is disposed in a unitary assembly removably received in the opening.
In accordance with yet another aspect of the present invention, a method of suppressing fluid-borne noise caused by pressure fluctuations in fluid flowing through a conduit includes sensing the amplitude and frequency components of pressure fluctuations in the conduit, and energizing a piezoelectric actuator as a function of the amplitude and frequency components so as to impart pressure fluctuations to fluid in the conduit. The actuator preferably is energized as a function of the frequency component of greatest amplitude, 180xc2x0 out of phase with such frequency component.